NAME

       SPI_prepare - prepare a statement, without executing it yet

SYNOPSIS

       SPIPlanPtr SPI_prepare(const char * command, int nargs, Oid * argtypes)

DESCRIPTION

       SPI_prepare creates and returns a prepared statement for the specified command, but doesn't execute the
       command. The prepared statement can later be executed repeatedly using SPI_execute_plan.

       When the same or a similar command is to be executed repeatedly, it is generally advantageous to perform
       parse analysis only once, and might furthermore be advantageous to re-use an execution plan for the
       command.  SPI_prepare converts a command string into a prepared statement that encapsulates the results
       of parse analysis. The prepared statement also provides a place for caching an execution plan if it is
       found that generating a custom plan for each execution is not helpful.

       A prepared command can be generalized by writing parameters ($1, $2, etc.) in place of what would be
       constants in a normal command. The actual values of the parameters are then specified when
       SPI_execute_plan is called. This allows the prepared command to be used over a wider range of situations
       than would be possible without parameters.

       The statement returned by SPI_prepare can be used only in the current invocation of the C function, since
       SPI_finish frees memory allocated for such a statement. But the statement can be saved for longer using
       the functions SPI_keepplan or SPI_saveplan.

ARGUMENTS

       const char * command
           command string

       int nargs
           number of input parameters ($1, $2, etc.)

       Oid * argtypes
           pointer to an array containing the OIDs of the data types of the parameters

RETURN VALUE

       SPI_prepare returns a non-null pointer to an SPIPlan, which is an opaque struct representing a prepared
       statement. On error, NULL will be returned, and SPI_result will be set to one of the same error codes
       used by SPI_execute, except that it is set to SPI_ERROR_ARGUMENT if command is NULL, or if nargs is less
       than 0, or if nargs is greater than 0 and argtypes is NULL.

NOTES

       If no parameters are defined, a generic plan will be created at the first use of SPI_execute_plan, and
       used for all subsequent executions as well. If there are parameters, the first few uses of
       SPI_execute_plan will generate custom plans that are specific to the supplied parameter values. After
       enough uses of the same prepared statement, SPI_execute_plan will build a generic plan, and if that is
       not too much more expensive than the custom plans, it will start using the generic plan instead of
       re-planning each time. If this default behavior is unsuitable, you can alter it by passing the
       CURSOR_OPT_GENERIC_PLAN or CURSOR_OPT_CUSTOM_PLAN flag to SPI_prepare_cursor, to force use of generic or
       custom plans respectively.

       Although the main point of a prepared statement is to avoid repeated parse analysis and planning of the
       statement, PostgreSQL will force re-analysis and re-planning of the statement before using it whenever
       database objects used in the statement have undergone definitional (DDL) changes since the previous use
       of the prepared statement. Also, if the value of search_path changes from one use to the next, the
       statement will be re-parsed using the new search_path. (This latter behavior is new as of PostgreSQL
       9.3.) See PREPARE(7) for more information about the behavior of prepared statements.

       This function should only be called from a connected C function.

       SPIPlanPtr is declared as a pointer to an opaque struct type in spi.h. It is unwise to try to access its
       contents directly, as that makes your code much more likely to break in future revisions of PostgreSQL.

       The name SPIPlanPtr is somewhat historical, since the data structure no longer necessarily contains an
       execution plan.